With the advent of swift and easy electronic transmission of written messages (e-mail, STM, etc.), the opportunity for Cantonese speakers to write Cantonese (in contrast to simply speaking that language) expanded vastly. The ease and speed of electronic communication of written messages encouraged a casual, conversational tone, so the old notion that writing was restricted to Mandarin began to break down much more rapidly than before. The problem, though, is simply that — even though they may want to write the way they speak — most young people are not adequately equipped with the special script resources necessary for writing the full range of spoken Cantonese. Consequently, there has arisen a clever style of writing Cantonese in a combination of the 3 languages and 2 scripts mentioned above.
Here is an example of how complex this style of written Cantonese can be (bear in mind that even this is not as "Cantonesey" as one might be if one pullled out all the stops): 好5舍得大学生活，E+就要离开了，有D接受5到呢个事实~~"I will transcribe and translate this later on. For the moment, please note that the writing is a combination of Roman letters, Arabic numerals, a mathematical symbol, and simplified characters, all representing Sinitic morphemes.
Only specialists in the writing of Cantonese can accurately convey the full range and nuances of relatively pure Cantonese, and even for them it is a challenge to find means to write (and especially to type) all the unique Cantonese morphemes that are regularly used in speech. Consequently, for those who are not specialists in written Cantonese, but only dabble in it, no matter how fluent and comfortable they may be in speaking Cantonese, they are likely to have to resort to such alphanumericized, Mandarinized hybrids as the one with which we started: 好5舍得大学生活，E+就要离开了，有D接受5到呢个事实~~"
Victor Mair at Language Log